Rabies 101
A New Scientist article from a few years back suggests that vampire legends were how our ancestors tried to explain rabies. Interesting to think of vampire stories as educational tools. 
Nowadays, of course, kids learn about rabies through Old Yeller, that “sick doggy snuff film”, to quote Phoebe from Friends.
[Rabies/vampires] is then analogous to [Williams Syndrome/elves]. The latter is a genetic disorder which causes elfin features and a love of music, clearly the inspiration for elves in various fairy tales.